1. Field of the Invention
The present invention relates to a pneumatic tire in which deterioration in wet performance of the tire due to wear of the tire can be suppressed.
2. Description of the Related Art
Conventionally, in pneumatic radial tires, especially tires for passenger cars, in order to improve the ground-contact performance, the wet performance, and wear resistance, and in order to reduce noise, a method in which sipes are provided in block-shaped land portions or in ribs formed on a tread surface of the tire has been employed. Accordingly, edge components can be increased, and the rigidity of the blocks can be controlled.
Ordinarily, in the case of improving wet performance, narrow sipes are formed in the block-shaped land portions. By making narrow sipes, the edge components can be increased and the rigidity of the block-shaped land portions can be ensured. However, in the case in which narrow sipes are formed in the block-shaped land portions, although the edge components can be ensured sufficiently, there is a problem with draining performance. Namely, in a tire having such sipes formed therein, at the initial stage of wear of the tire, sufficient draining performance can be obtained by main grooves or the like which are formed in the tread surface. However, in a later stage of wear of the tire, because the draining performance of the main grooves or the like deteriorates, the sipes must also exhibit the ability to drain. However, if the sipes are narrow, the draining performance is low, and it is thus difficult to ensure a sufficient wet performance.
In order to improve the draining performance of the sipes, it is desirable to increase the widths of the sipes. However, in this case, there is the concern that the rigidity of the blocks may decrease, and accordingly, the stability and controllability performance may deteriorate greatly. Further, if the width of the sipe is increased, the amount of noise may increase.
A tire in which sipes are made wider only at portions of the sipes which are exposed in the final stage of wear of the tire has been proposed. However, with this tire, there is the drawback that the draining performance of the sipes deteriorates at the intermediate stage of wear and the wet performance deteriorates.